Bug#863290: src:linux: no warning that btrfs RAID5/6 is buggered up
On 4 June 2017 at 05:46, Svein Engelsgjerd <waxhead@dirtcellar.net> wrote:
>
> I would like voice my concern as well. Btrfs RAID5/6 really needs a warning.
> These days most (if not all) of the problems you see with Btrfs is caused by
> the unstable features (https://btrfs.wiki.kernel.org/index.php/Status).
>
> RAID5/6 in kernel 4.9 is less than stellar and should absolutely not be used
> for anything except testing and experimentation.
+1 It's been well known that it causes problems since before
2016-06-26, and the consensus on the upstream btrfs mailing list is
that in the absence of an unexpected and heroic feat reliable raid5/6
profile is years away from completion.
> RAID1 actually needs a warning too. It will not work as "classic" RAID1 e.g.
> it need to be able to make two copies always to not get stuck in read only mode.
> You will not loose your data which is a good thing, but to be safe you need a
> minimum of 3 devices (I would prefer four or more to be on the safe side).
Do you mean that btrfs raid1 profile (assume raid1 profile for both
data and metadata) is 2 copies on n devices? Adding more devices to
the volume does not increase copies or reduce risk; it increases the
size of the volume, but there are still only 2 copies on two different
devices. As things stand, n-way raid1 profile will not be worked on
until work on raid5/6 profile is in a good state, so many, many years
out.
I've updated the TODO items at https://wiki.debian.org/Btrfs to
explain this in more depth and will write the new sections when I have
a long enough chunk of free time to streamline the article for
Stretch's release. If there is anything anyone feels should be on our
btrfs wiki page, please let me know so that I can add it to the queue,
or alternatively add it directly to the TODO items. Also, if there is
anything in that article that seems like it should be moved to the
upstream wiki I would be happy to do that.
Cheers,
Nicholas
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